As Bill says; for freewheels, clamping the tool in a heavy duty bench vice - attached to a heavy bench - is the best way to remove them. Leave the tire on, and inflate to maximum recommended pressure for something to grip on to. And triple check that your trying to go in the correct direction - opposite of the what the chain pulls the gears when you are riding.

Hmmm, I appreciate your feedback. However, I'm pretty sure it's a cassette. I thought most modern mid-high end bikes came with cassettes rather than freewheels nowadays?

Anyway, let me give you all a bit of background to my cassette saga.

I actually tried removing my cassette without the use of a chainwhip, where I simply held the cassette in place with a rag & turned the adjustable wrench/cassette tool, just to see if it would work because I didn't have a chainwhip up until this weekend just gone.

Anyway, the cassette did loosen & I managed to slide it off, but there was no freehub body to be found underneath it! I'm fairly sure it was lodged inside the cassette still!

So I put the cassette back on, re-tightened it with my wrench/cassette tool and it made kind of strange, crunching sound as I did this. What I can only assume to be the splines of the cassette 'ratcheting' back on. Bear in mind, I had to use a lot of force for it to make this noise. Otherwise, the cassette just wouldn't re-tighten at all.

Meanwhile, I went to one of the LBS in my area to buy a chainwhip a couple of days ago and while I was there I explained what had happened to the mechanic in the workshop. He said, that Mavic wheels are designed like this, so that you can remove the cassette without necessarily exposing the freehub body. Sound strange? It did to me. So he told me I would need a chainwhip to be able to remove the cassette from the freehub.

This is what I've been trying to do, obviously to no avail.

Apologies for such a lengthy post. I just want to provide all the info I can.

I would post pictures, but I don't think that would convey whatever the issue is, because there doesn't look anything untoward or out of place just to look at it. I can though, if any of you wish.